An Investigation of Surface Inversion Characteristics in Shallow Topography

Stable boundary layers are not well understood, and they continue to be a difficult subject to model. Within the stable boundary layer, surface temperature inversions may be present. Because of this, pesticide drift, or unintentional diffusion of pesticides, may occur if an inversion is occurring at the time of application. Despite labels on pesticides that explain not to apply during this time, drift continues to damage property, human health, and the environment. In addition, the effects of shallow topography, which is common in farmlands in the Midwest, and cold air drainage on inversion strength and persistence has not been studied. This research focuses on the mechanisms present at the time prior to inversion and utilizes data taken from the Stable Atmospheric Variability and Transport (SAVANT) field project located in Mahomet, Illinois. Four towers within a shallow drainage gully measured wind speed and temperature throughout the study at up to eight different heights. Statistical analysis of the characteristics of inversions was done, with focus on the variation caused by cold air drainage at the lower areas of the gully. While prior studies showed most inversions in stable and very stable conditions occur below a threshold value of 2 m/s, many of the stronger inversions (5°+ C from 1.5 to 20 m) occurred with wind speeds at 5 m/s at 20 m. Temperature differences and persistence were generally longer down gully, with the longest lasting over 13 hours from prior to sunset until well after sunrise.